A typical prior art method of single side band generation, which may be a filtering method, applies a modulating signal to a first carrier frequency via a balanced modulator, then filters the result to provide a single side band signal which is then mixed by adding to a second carrier frequency to obtain, as a desired output, a single side band signal at the sum of the two carrier frequencies.
Another prior art method of single side band generation involves phasing of first carrier and modulating frequencies to cancel out the carrier in one of the side bands and mixing the resulting side band signal by addition with a second carrier frequency to obtain, as the desired output, a side band signal at the sum of the two carrier frequencies.
Another prior art method has involved balanced modulation and add mixing to obtain the desired frequency, followed by either filtering or phasing out of the carrier in one side band before applying the generated single side band signal to a linear amplifier for output. In this latter method the output signal is the side band frequency of the carriers.
Thus, in summary, prior known methods of single side band generation have utilized the first carrier signal as an integral part of the output frequency of the single side band generator. Thus, single side band transmitters utilizating sum frequencies carry the distortion (frequency, phase, and inter-carrier) that exists on the first carrier, or because of such first carrier, into the linear amplifier for amplification and transmission.
The objects of this invention include provision of single side band apparatus to remove the first carrier frequency from the generated and filtered side band frequency after the signal has been mixed with a second radio frequency to obtain what would normally be the single side band output frequency.
A further object of this invention is to provide an apparatus as aforesaid for thus eliminating distortion due to the first carrier, and to permit the use of CW/AM frequencies of a transmitter, without frequency modifications, for side band operation.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.